With the advancement of high-density mounting in electronic equipment, various surface mount electronic components are used these days. Some electronic component chips need hermetic sealing. To encase such an electronic component chip, a surface mount electronic component including a resin case that has a hollow casing part has been used in the art.
FIG. 8 is a perspective view that illustrates the mounting structure of a surface mount electronic component disclosed in the patent literature (PTL) 1 shown below. A surface mount electronic component 1001 is mounted on a substrate 1002. Electrodes 1003 and 1004 are formed on the substrate 1002. The metal terminals 1005 and 1006 of the surface mount electronic component 1001 are bonded to the electrodes 1003 and 1004 by means of solder blobs 1007 and 1008, respectively. A reflow soldering method is used for the bonding.
The surface mount electronic component 1001 has the following structure: a top cover member 1010 is bonded to an open-topped case body 1009; a bonding material 1011 is sandwiched between the cover 1010 and the case 1009 to fix them to each other. Therefore, the surface mount electronic component 1001 has a casing structure that includes an inner space functioning as a casing space. An electronic component chip that is not illustrated is encased in this hollow casing part. The metal terminals 1005 and 1006 are connected to the electronic component chip.
When the surface mount electronic component 1001 is mounted to the substrate 1002 by using the reflow soldering method, solder is heated to a temperature at which it melts, for example, approximately 260° C. The internal pressure of the surface mount electronic component 1001 increases due to heating. In order to prevent the case from being damaged due to the increase in the internal pressure, a through hole 1012 is formed as illustrated in FIG. 9. The hole 1012 is formed through a sidewall of the case body 1009. The metal terminal 1005 extends from inside the through hole 1012 onto the bottom surface of the case body 1009 by way of the side surface thereof. In the process of the rising of the internal pressure due to heat applied at the time of reflow soldering, air escapes from the inside of the case body 1009 to the outside through the through hole 1012. By this means, it is possible to prevent the internal pressure of the case from increasing significantly. After heating during the process of reflow soldering, the mounted component is allowed to cool to room temperature. In the cooling step, the solder 1007 that is in a molten state hardens. As a result, as illustrated in FIG. 9, the metal terminal 1005 and the electrode 1003 become bonded to each other. Since a part of the solder 1007 in the molten state flows into the through hole 1012, the through hole 1012 gets sealed as a result of the solidification of the molten solder. Therefore, the case that has been subjected to reflow soldering is hermetically sealed.
PTL 1: Japanese Unexamined Patent Application Publication No. 2006-294757